1.2 Pharmacokinetic Factors Determining Drug Action
Route of administration
The drug (oral medication) is ingested via the mouth.
Absorption & distribution
The medication travels down the esophagus into the stomach, where acids break it down.
From there, the drug’s molecules are absorbed into the bloodstream that nourishes the intestinal
tract and stomach. An empty stomach will absorb the drug much faster than a full one will. Once
the drug enters the circulatory system, it passes through the liver on its way to the central
nervous system (CNS). As the drug goes through the liver, the liver metabolizes (inactivates) it,
effectively decreasing its potency (by roughly 25%) before it enters the CNS. This process is
known as the “First Pass Effect.” Selective barriers, including the blood brain barrier (BBB) and
placental barrier, limit the distribution of the drug into the CNS.
The BBB protects brain tissue and neurons from dangerous molecules that could disrupt
and dysregulate brain functioning. It selectively allows molecules (drugs and nutrients) to enter
the brain while removing waste via a network of capillaries (small blood vessels). The molecules
then selectively pass through the capillaries’ intracellular clefts (small gaps) and fenestrations
(larger openings). Pinocytotic vesicles (larger capillaries) envelope and transport the molecules
across the BBB and into the brain tissue itself. If the brain detects any toxic substances in the
bloodstream, it will trigger the area postrema (AP) in order to expel the toxic substances before
they are taken into circulation by the blood vessels and protect the organism (the individual
taking the drug). The activation of the AP induces vomiting.
Route of administration
The drug (oral medication) is ingested via the mouth.
Absorption & distribution
The medication travels down the esophagus into the stomach, where acids break it down.
From there, the drug’s molecules are absorbed into the bloodstream that nourishes the intestinal
tract and stomach. An empty stomach will absorb the drug much faster than a full one will. Once
the drug enters the circulatory system, it passes through the liver on its way to the central
nervous system (CNS). As the drug goes through the liver, the liver metabolizes (inactivates) it,
effectively decreasing its potency (by roughly 25%) before it enters the CNS. This process is
known as the “First Pass Effect.” Selective barriers, including the blood brain barrier (BBB) and
placental barrier, limit the distribution of the drug into the CNS.
The BBB protects brain tissue and neurons from dangerous molecules that could disrupt
and dysregulate brain functioning. It selectively allows molecules (drugs and nutrients) to enter
the brain while removing waste via a network of capillaries (small blood vessels). The molecules
then selectively pass through the capillaries’ intracellular clefts (small gaps) and fenestrations
(larger openings). Pinocytotic vesicles (larger capillaries) envelope and transport the molecules
across the BBB and into the brain tissue itself. If the brain detects any toxic substances in the
bloodstream, it will trigger the area postrema (AP) in order to expel the toxic substances before
they are taken into circulation by the blood vessels and protect the organism (the individual
taking the drug). The activation of the AP induces vomiting.
